1. Field of the Invention
This invention involves an apparatus and method for measuring light energy output from optical fibers, and more particularly for measuring backscatter fluorescence from the distal end of an optical fiber as a means for calculating light energy output.
2. Description of Related Art
Optical fibers can be used as a means of transmitting light energy from a generator light source to a target. A certain amount of light energy loss occurs in the optical fiber due to absorption and coupling losses with the light source at the proximal end. The absorption loss may not be uniform along the length of the fiber. The amount of absorption also varies with the length of the fiber. Because of the variability of energy absorption and coupling losses, output energy will not be the same as input energy from the generator light source.
Optical fibers are increasingly used with laser light sources, particularly in medical applications. In the past, output energy often has not been controlled. Instead, a particular "on" time and power level of the input laser energy have been selected, with monitoring of the results obtained by the output energy being qualitatively determined by such means as fluoroscopy. These optical fibers are used without any real energy output feedback system; the output energy is adjusted through trial and error. This creates a hazardous and even dangerous condition in situations where energy output should be measured precisely, such as within the human body.
One feedback system which does exist (as described in U.S. Pat. No. 4,648,892) measures backscatter fluorescence from laser light reflection off target material, back through the optical fiber. The energy output is then calculated from this backscatter fluorescence. The problem with this method of feedback control is that different target materials reflect spectral light differently. In addition, the amount of target material or the presence of more than one type of material in the target area will also cause different amounts of fluorescence. Therefore, calibration can be a significant problem, especially if the target material is within the human body. Thus, there is still a real need in the current art for a system of accurately measuring energy output from an optical fiber, particularly a laser optical fiber.